"The National Party had a memorandum of understanding with the Green Party."

She's talking about the Greens and National's 'shared policy initiatives' agreement of 2009, when the rivals set aside their differences to get houses insulated and work on energy efficiency.

Seven years later, the Greens have signed a deal with Labour to work together to wrest power from National, after refusing to do so at the previous two elections.

"This one is around us working together cooperatively up to the election because we want to change the Government. That won't please everybody… but it's what we've decided to do."

Ms King says it's better than "just having a cup of tea down somewhere in Auckland a week before the election".

It had become something of an election cliche for the leader of the National Party to sit down with the leader of ACT for a cup of tea in Epsom. A quirk in MMP meant in order to maximise the chances of a National-led Government, it was better if ACT won the seat instead of National.

That tradition ended following the tea tape scandal of 2011.

Though the tea is no longer brewing, Ms King says National has effective MOUs with not just ACT, but also "bland" Peter Dunne and the Maori Party.

"If they didn't have those two, they wouldn't make up the Government."

National MP Nikki Kaye says the word from the business community is an alliance between Labour and the Greens would be "far too left", and she expects the MOU to unravel in time.